1. Field of the Invention
This invention relates broadly to a torsion bar assist system for opening access doors and particularly to a torsion bar assist system for heavy access doors used to cover underground utility vaults.
2. Description of the Prior Art
The use of a torsion bar assist system for hatchway doors is known and described in U.S. Pat. No. 3,067,453. This patent describes a hatchway cover assembly in which the counterbalancing torsion rods serve the dual function of pivotally hinging a door to the frame as well as exerting a counterbalancing force on the door to facilitate movement thereof.
Access covers for utility vaults have generally been designed to open to a vertical position relative to the plane of the opening; however, the industry has desired an access door which can be laid back flat adjacent the opening so that electrical cable can be pulled and the job accomplished without interference from the upstanding doors.